Gas turbines with sequential combustion are known and have proved to be successful in industrial use. Such a gas turbine, which has been known among experts as GT24/26, follows, for example, from an article by Joos, F. et al., “Field Experience of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family”, IGTI/ASME 98-GT-220, 1998 Stockholm. In this document, FIG. 1 shows a basic construction of such a gas turbine. FIG. 1 of the Joos document is reproduced in the present disclosure as FIG. 1. Furthermore, such a gas turbine follows from EP-B1-0 620 362.
As shown in FIG. 1, the stator blades 10 of the known gas turbine have a blade airfoil 11 which extends in the longitudinal direction and which is delimited in the flow direction of a hot gas (parallel arrows in FIG. 1) by a leading edge 14 and a trailing edge 15. In the longitudinal direction, the blade airfoil 11 is delimited by a blade tip 13 and a cover plate 12 (sometimes also referred to as a shroud). The blade tip 13 delimits the annular hot gas passage of the turbine on the inner side and can adjoin the rotor shaft of the turbine via a sealing segment. The shroud 12, by its inner side 19, delimits the hot gas passage on the outside.
On the outer side of the shroud 12, which is exposed to throughflow by a cooling medium (for example, cooling air), a front and rear hook-like fastening element 16 or 17 are formed, which on the one hand serve for the fastening of the stator blade 10 on the inner casing of the turbine, and on the other hand are available for the locating and fixing of adjacent heat accumulation segments (“heat shields”; see FIG. 2, ref. no. 24) in the flow direction. For this purpose, on the rear fastening element 17, provision is made for a locating slot 18 into which a heat shield can be inserted. The locating slot 18 is delimited towards the shroud 12 by means of a horizontal base surface 18′ which, together with the inclined inner side 19 of the shroud 12, forms a wedge-shaped section 19′ in the region of the trailing edge 15, which section is characterized by a large material volume.
The transition 21 between the trailing edge 15 of the stator blade 10 and the shroud 12 represents a region for the service life of the stator blade 10, since a high thermal stress, which results from a thermal-mechanical mismatch between the shroud 12 and blade airfoil 11, is established within the region, wherein this leads to a peak in the mechanical stress, which results from the stress of the blade airfoil 11 which is impinged upon by the hot gas flow, being superimposed. The large material volume, which is mentioned above, in the wedge-shaped section 19′ above the trailing edge 15 can lead to a significant increase of the thermal stresses in this region, which is important for the service life of the stator blade 10, and can therefore lead to a reduction of the service life itself, bearing in mind the fact that modern gas turbines require high temperatures with respect to operating fluids, which in many cases lie beyond the permissible material temperature of economically usable materials.